Mechanisms of the recognition of degenerating dendrites

项目摘要/摘要 神经元突起的局部变性是神经回路重塑和损伤的重要机制。 神经元损伤。变性产生的神经元碎片必须被吞噬细胞迅速清除，以 防止炎症和促进随后的神经元再生。尽管异常的认知和 清除神经元碎片与神经炎症、自身免疫和神经退行性变有关 对于疾病，吞噬细胞如何区分退化的轴突和周围的健康轴突，目前尚不清楚。在……里面 特别是，有三个重要的问题仍然没有得到回答：关于退行性轴突的信号是什么 能被吞噬细胞识别吗？变性神经突起识别信号的受体是什么？ 在变性的神经突起上，识别信号是如何具体暴露的？我们新的活体数据提供了 帮助我们解开这些谜团的重要线索。使用我们新的体内探测器，我们发现 ‘Eat-Me’信号磷脂酰丝氨酸(PS)在健康树突表面不存在，但暴露在 发育重塑和身体损伤中的退化树突。以这些观察为基础， 本项目旨在阐明PS在树突中暴露和识别的体内机制 以果蝇感觉神经元为模型系统的退行性变。我们的长期目标是发现 树突变性和修复的自主和非自主机制。对于这个项目，我们 提出以下三个目标：1)确定PS暴露在识别和吞噬中的作用 退化的树突。损伤后吞噬树突的PS暴露的必要性 通过(I)用PS结合蛋白掩蔽树突表面的PS，以及(Ii)阻断 PS在特定神经元中的生物合成。PS触发树枝晶吞噬的充分性 变性将通过异位诱导神经元PS暴露来测试。2)调查CED-1如何 家庭成员德雷珀认出了退化的树突。我们的结果表明德雷珀认识到 退化的树突。将进行两项互补的体内竞争分析，以确定 Draper直接与PS交互。3)确定神经元中PS暴露是如何调节的，以及 退化的树突。通过对候选基因进行功能丧失研究，PS的身份 在树突退化过程中调节PS暴露的翻转酶和扰乱酶将被确定。这个 Caspase在PS暴露中的作用将通过检测树突损伤后的caspase活性和通过 破坏神经元中的半胱氨酸天冬氨酸酶途径。总之，这些目标将揭示神经元的体内机制 碎片感应系统。因为哺乳动物和昆虫清除神经元碎片需要相同的CED-1 吞噬受体家族，这项研究将揭示保守的机制，可能与 神经退行性疾病。

Project Summary/Abstract Local degeneration of neuronal processes is an important mechanism in neural circuit remodeling and neuronal injury. The neuronal debris resulting from degeneration must be promptly cleared by phagocytes to prevent inflammation and to facilitate the subsequent neuronal regrowth. Although aberrant recognition and clearance of neuronal debris are implicated in neuroinflammation, autoimmunity, and neurodegenerative diseases, it is unknown how phagocytes distinguish degenerative neurites from surrounding healthy ones. In particular, three important questions remain unanswered: what is the signal on degenerating neurites that allows the recognition by phagocytes? What is the receptor for the recognition signal of degenerating neurites? How is the recognition signal specifically exposed on degenerating neurites? Our new in vivo data provided important clues that will help us to solve these puzzles. Using our new in vivo probes, we discovered that the ‘eat-me’ signal phosphatidylserine (PS) is absent on the surface of healthy dendrites but is exposed on degenerating dendrites in both developmental remodeling and physical injury. Building on these observations, this project aims to elucidate the in vivo mechanisms of PS exposure and recognition in dendrite degeneration using Drosophila sensory neurons as a model system. Our long term objective is to uncover autonomous and non-autonomous mechanisms of dendrite degeneration and repair. For this project, we propose the following three aims: 1) Determine the role of PS exposure in the recognition and engulfment of degenerating dendrites. The necessity of PS exposure in engulfment of dendrites after injury will be determined by (i) masking PS on the dendrite surface with PS-binding proteins, and (ii) blocking the biosynthesis of PS in specific neurons. The sufficiency of PS in triggering dendrite engulfment and degeneration will be tested by ectopically inducing PS exposure in neurons. 2) Investigate how the CED-1 family member Draper recognizes degenerating dendrites. Our results suggest that Draper recognizes degenerating dendrites. Two complementary in vivo competition assays will be performed to determine if Draper directly interacts with PS. 3) Determine how PS exposure is regulated in neurons and degenerating dendrites. By conducting loss-of-function studies of candidate genes, the identities of PS flippases and scramblases that regulate PS exposure during dendrite degeneration will be determined. The role of caspases in PS exposure will be investigated by examining caspase activity after dendrite injury and by disrupting the caspase pathway in neurons. Together, these aims will reveal in vivo mechanisms of neuronal debris sensing. As the clearance of neuronal debris in both mammals and insects requires the same CED-1 family of engulfment receptor, this study will reveal conserved mechanisms that may be relevant to neurodegenerative disorders.